Method and apparatus for controlled size distribution of gel microspheres formed from aqueous dispersions

Abstract

The present invention is directed to a method and apparatus for making a population of dense, closely size-controlled microspheres by sol-gel procedures wherein said microspheres are characterized by a significant percentage of said population being within a predetermined, relatively narrow size range. Microsphere populations thus provided are useful in vibratory-packed processes for nuclear fuels to be irradiated in LWR- and FBR-type nuclear reactors.

What is claimed is: 
     
       1. A method for controlling the size range distribution of a sol-gel prepared spheroidal product wherein the formed spheroids are in a diameter range up to about 300 microns and wherein about 90 percent of the spheroid population is selectively formed in a narrow predetermined size range within said diameter range, comprising the steps of admixing globules of an aqueous dispersion of at least one metal value and a sol-forming agent with a water immiscible organic liquid, introducing the admixture into a column having a series of right-handed helical elements joined together at right angles to one another and mechanically affixed to inner walls of said column to provide a tortuous passageway therethrough for mechanically inducing sufficient turbulence in the admixture for disrupting laminar flow of the admixture in the column and for subjecting said admixture to adequate uniform agitation throughout the cross section of the column to effect the formation of substantially uniform-sized droplets of the aqueous dispersion in the column, maintaining the droplets in said column under the influence of the agitation for a sufficient duration to initiate gelation of the droplets, and conveying the formed droplets into a gelation column containing the water-immiscible organic liquid to effect further gelation of the droplets and form said spheroids. 
     
     
       2. The method claimed in claim 1, wherein the metal value is a salt or oxide of uranium, thorium, plutonium, or combinations thereof. 
     
     
       3. The method claimed in claim 1, wherein the sol-forming agent is urea or hexamethylene-tetramine. 
     
     
       4. The method claimed in claim 1, wherein the water-immiscible organic liquid is trichloroethylene, 2-ethyl-1-hexanol or iso-amyl alcohol. 
     
     
       5. The method claimed in claim 1, including the additional step of selectively varying the flow rate of the admixture through the column having a tortuous passageway therethrough for selectively varying the size range distribution of the spheroids formed therein. 
     
     
       6. The method claimed in claim 5, wherein the step of selectively varying the flow rate of the admixture comprises increasing the velocity of the admixture through the column having a tortuous passageway therethrough for forming the majority of spheroids of smaller uniform size.